Recently, a technique termed Open-Flow has been proposed (see Patent Literature 1 and Non-Patent Literatures 1 and 2). The OpenFlow comprehends communication as an end-to-end flow and effects path control, recovery from malfunctions, load distribution and optimization on the flow-by-flow basis. The OpenFlow switch, operating as a relaying device, includes a secure channel for communication with an OpenFlow controller that is to operate as controller. The OpenFlow switch is in operation in accordance with a flow table the addition in or the rewriting of which is commanded from time to time by the OpenFlow controller. In the flow table, a set of a matching rule (header field) for matching against a packet header, flow statistics information (Counters) and actions, are defined on the flow-by-flow basis (see FIG. 9). The actions define contents of the processing applied to the packet that has matched to the matching rule (Header Fields).
On receipt of a packet, the OpenFlow switch retrieves the flow table for an entry having the matching rule that matches to the packet's header information (see the header field of FIG. 9). If, as a result of the retrieval, the entry that matches to the incoming packet has been found, the OpenFlow switch updates the flow statistics information (Counters). The OpenFlow switch also applies to the incoming packet the processing of contents stated in an action field of the entry, such as transmission of the packet from the specified port, flooding or discarding (drop). If, as a result of the above mentioned retrieval, no entry that matches to the incoming packet has been found, the OpenFlow switch forwards the incoming packet to the OpenFlow controller, over the secure channel, with a request to the controller to decide on a forwarding path for the packet based upon the source as well as the destination of transmission of the incoming packet. The OpenFlow switch then receives the implementing flow entry to update the flow table. In this manner, the OpenFlow switch forwards the packet, using the entry, stored in the flow table, as the set of packet handling operations.
In Patent Literature 2, there is disclosed a relaying device including a port movement circuit for detecting port movements that will take place in case a frame has arrived via a path other than a learned path in a MAC address table.
[Patent Literature 1]    W02008/095010A1 Pamphlet
[Patent Literature 2]    JP Patent Kokai Publication No. JP2008-301003A
[Non-Patent Literature 1]    Nick McKeown et al., “OpenFlow: Enabling Innovation in Campus Networks”, (online), (retrieved on Jul. 6, 2010), Internet <URL: http://www.openflowswitch.org/documents/openflow-wp-latest.pdf>
[Non-Patent Literature 2]    “OpenFlow Switch Specification” Version 1.0.0. (Wire Protocol 0x01) (retrieved on Jul. 6, 2010), Internet <URL: http://www.openflowswitch.org/documents/openflow-spec-v1.0.0.pdf>